Electron emitter



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E umm w j 2 7 w Aug. 9, 1955 J. D. REID ELECTRON EMITTER Filed Feb. 21,1946 United States Patent O ELECTRON EMITTER John D. Reid, Oak Ridge.Tenn., assgnor, by mesne assignments, to the United States of America asrepresented by the United States Atomic Energy Commission ApplicationFebruary 21, 1946, Serial No. 649,404

1 Claim. (Cl. 313305) This invention relates to electron emissive andrelated devices, and it is particularly concerned with a secondaryelectron emitter, that is, a secondary emitter which is renderedemissive by being heated as a result of being bombarded by electronsemitted from a primary emitter. The invention finds particularadaptability in ion sources ordinarily used in calutrons, that is, inthe electromagnetic type of apparatus which is used for separatingisotopes. ln this type of ion source, a vapor of a material the isotopesof which are desired is bombarded in an ionization chamber by electronsemitted by an emissive device. In calutrons it is often desirable to usea primary and secondary emitter. The secondary emitter produces thestream of electrons which bombards the vapor in the ionization chamber.The secondary emitter is subject to conditions which experience hasshown tends to make it very short lived requiring frequent replacementand renewal.

The primary object of my invention is to provide a secondary emitterhaving characteristics calculated to give it longer life and to make theemitter extremely easy of replacement and renewal.

Another object of my invention is to provide a secondary emitter of thetype referred to above so constructed and arranged as to provide for themaximum of ease in assembly and disassembly.

Another object of my invention is to provide a secondary emitter havingvery simple, convenient, efficient, and easily fabricated means forinsulatively mounting the emitter.

Another object of my invention is to provide a secondary emittercomprising a yoke having apertures in the arms thereof with a transversemember having its ends tted into the apertures, the arrangementproviding for removal and replacement of the transverse member byspringing apart of the arms of the yoke.

Another object of my invention is to provide an arrangement as in thepreceding object wherein the yoke is made of molybdenum and thetransverse member is of tantalum.

Another object of my invention is to provide a mounting for a secondaryemitter or the like consisting of screws and Lavite nuts, the nuts beingcountersunk in the base member upon which the emitter is mounted.

Further objects and numerous of the advantages of my invention willbecome apparent from the following detailed description and annexeddrawing wherein Fig. l is a front View of the emitter of my invention.Fig. 2 is a sectional side elevation of the emitter of Fig. l takenalong line 2-2 of Fig. l, and Fig. 3 is a diagrammatic perspective viewshowing a primary emitter, the secondary emitter of my invention and ananode in the relative positions which they would normally occupy.

Referring to Fig. 1 of the drawing, the emitter comprises a stainlesssteel strip of metal 3 which is bent at its upper end as shown in Fig.2, and attached to the upper end of this strip by soldering or the likeis a U-shaped yoke member 2 which is made of molybdenum.

2,715,196 Patented Aug. 9, 1955 ICC The arms of the yoke member haveapertures as shown at 9 and fitting in these apertures are the ends of atransverse rod member 1 the ends of which are tapered. The rod 1constitutes the electron emissive element, it being made of tantalum. Itwill be noted that one end of the rod 1 has a slightly longer taper thanthe other end, and the arms of the yoke 2 are suiciently resilient topermit of springing them apart for easily removing the rod 1 andreplacing it with a new one.

The plate 3 is attached to a base or panel 10 by means of a flat-headedscrew 6 and a round-headed screw 7, the flat-headed screw 6 extendingthrough an elongated opening 11 as may be seen on Fig. l. Theround-headed screw 7 extends through an enlarged opening 12 and a washer13 is between the head of the screw and the plate 3 as shown. Due to theopening 12 being larger than the screw 7 and the opening 11 beingelongated, when the screw 7 is loosened, the plate 3 can be adjusted upand down and then resecured. The screws 6 and 7 screw into nuts 5 and 14which are made of a suitable insulating material and each of which is inthe shape of a truncated cone, the nuts being counter-sunk incorrespondingly shaped countersinks in base or panel 10. Numeral 8designates a strip of insulating material which is interposed betweenthe plate 3, the panel 10 having openings therein through which thescrews 6 and 7 pass. In this manner the plate 3 of the emitter issecurely attached to the base 10 and is kept insulated therefrom, therebeing no protruding parts, particularly parts of insulating materialprotruding from the face of the panel 10. That is, the nuts 5 and 14 fitcompletely into the countersinks and are therefore protected frombreakage.

Referring to Fig. 3, the secondary emitter of my invention is shownadjacent the primary emitter 15, that is, a iilamentary cathode whichhas a voltage V impressed across the terminals thereof. A grid in theform of a plate 18 having a slot as shown is between the primary andsecondary emitters. Primary emitter 15 emits a stream of electrons whichbombards the tantalum rod 1 of the secondary emitter after passingthrough the slot of grid 18, thereby raising the temperature of rod 1suiciently to render it emissive, and it in turn emits a stream ofelectrons which, in the diagrammatic representation of Fig. 3, bombardsan anode or anode plate 16 supported by a stem 17. In applications wherethe secondary emitter is subject to severe conditions of usage resultingin rapid erosion and short life of the emitter, my invention isparticularly useful for the reasons pointed out in the foregoing in thatthe replacement and renewal is extremely easy, being eected simply byspreading the arms of the yoke 2 apart, removing the eroded rod 1 andreplacing it with a new one.

Both the vertical and horizontal adjustment of the secondary emitter canbe conveniently made, simply by loosening the screws 6 and 7 and thenmoving the strip 3 upwardly for vertical adjustment or rotating it aboutthe screw 6 for horizontal adjustment.

From the foregoing those skilled in the art will observe that I haveprovided a very convenient and efficient device adapted for use as asecondary emitter or in other ways as an electron emissive device. Thearrangement of my invention provides for quick and convenientreplacement and is mounted in a manner providing for very effectiveinsulation of the emitter and adjustment thereof.

The embodiment of my invention disclosed herein is representative of itspreferred form. The disclosure is to be interpreted in an illustrativerather than a limiting sense, the scope of the invention beingdetermined Ain=V accordance with the claim appended hereto.

I claim:

In electromagnetic isotope separating apparatusgxion-` 3 4 producingrmechanism vcomprising an electron emissive 849,159 Parker Apr. 2, 1902filame'ntiny the form of a cylindrical tantalu'r'n rod hav- 1,816,194Power July 28, 1931 ing tapered ends, the taper on one of said endsbeing 2,030,435 Fehse et al. Feb. 11, 1936 longer than the taper ontheother of said ends, means 2,171,238 Gustin Aug. 29, 1939 v forrbombardi'ng said filament with 'electrons to heat said 5 2,350,270Atlee May 30, 1944 filament to electron emissive temperature, and a yokemember of molybdenum having apertures in Vthe legs REFERENCES thereofforreceivng the tapered ends of said filament, General EleCUC RCVIeW,M3rCh1923, PP- 154-160- said yoke'rnember being resilient to provide forspringing'. apart the legs thereof to facilitate removal and re- 10placement of said rod.

References Cited in the le of this patent UNITED STATES PATENTS 258,976Bernstein June 6, 1882

